1. Field of Invention
The present invention relates to the correction of coordinate measuring errors in CMMs due to vibrations of the component parts thereof.
2. Description of the Related Art
U.S. Pat. Nos. 5,594,668 & 5,610,846, both assigned to Carl-Zeiss of Germany describe methods that use machine acceleration information with the aid of correction tables to determine the amount of displacement of the probe head due mainly to probing force.
In accordance with the description in these patents, the acceleration information in the three translation directions is obtained by double differentiating scale information. This gives the acceleration of the CMM at the measurement scales and not at the probe head.
Also in the methods described in the above-mentioned patents, a correction table containing prior knowledge of the bending behaviour of a particular CMM due to various accelerations and velocities at various positions is used to provide a correction to measurements obtained from the scales.
Another U.S. Pat. No. 5,579,246 assigned to Carl-Zeiss of Germany describes a method that has a similar goal, that is improving measurement accuracy with the aid of accelerometers located near or in the probe head. However the technique described requires a mathematical model describing the dynamic behaviour of the CMM within its measurement volume. Information gathered from the accelerometers are used as input to the model, the model then produces an estimate of the structural vibration, and thus the displacement of the probe head from its nominal axis.